This page has 2 parts:

Part 1 Dyno Chart Basics

& Part 2 Dyno Tuning Basics



Dyno Chart Basics
Dan Kyle


Dynamometers are a tool, and like any tool they can be used correctly or incorrectly.
When the results of an incorrect use are viewed by someone who is not familiar with the dynos operation, the results can be anywhere from misleading to a flat out lie.

Below is one of the more common ones:

This chart shows a ZX10R with a Sato slip-on, it is the same bike with no changes, EXCEPT the runs are done in different gears.  Using 3rd, 4th, and 5th gears, it appears that the runs are different, but actually it is the scale that has made them appear different. Look at the bottom of the graph, it uses MPH instead or the more correct RPM. Since different gears were used the MPH is of course different, this moves the graph line for each run to the right or left. But the curves are the same as is the peak HP. The fact that different gears where used also shows up as each run ends at a different MPH, exactly what one would expect.

Click to enlarge

Below is the same three runs shown with the correct RPM used as the bottom scale. In this case what gear the bike was in does not matter as we are just reading RPM and HP.

click to enlarge

Anytime you see a set of runs and MPH is used on the bottom scale, look
carefully to see that the MPH ends at the same speed, if it does not, they
have used different gears and are pulling a fast one.

Below is a good example:

In this example two different gears were used, showing how much better their exhaust is, when in reality, it appears the stock system may have made more HP.

click to enlarge


Dyno Tuning Basics
by Michael Wheeler

This next part started as a post I did on a forum, but I think it is relevant information & overlooked or misunderstood by many so I am going to display it permanently here

Dynojet has developed a way to interface their top of the line Dyno with their latest Powercommander products.

Now first & foremost the Powercommander basically only enhances what is already there based on the power delivery characteristics of the installed exhaust system. A good power curve from a quality exhaust will get better, but a bad power curve from a poorly designed exhaust is still going to be a poor curve even if it is improved upon. What we have seen time & time again is that good gains can be improved to a higher degree than poor gains can be improved. Exhaust dynamics is a tricky business, but if the flow is improved & the reversion waves are tuned properly then more fuel can be added & the more fuel you have the more power you get. If you have to remove fuel due to a poor flow design or the reversion waves are kicking back to the cylinder & meeting the next exhaust pulse at any point in the rev range then you simply are not going to get good power gains at that point. (that does not mean that a lean map is a bad one as sometimes the ECU's are just overich & the A/F has to be leaned out to become optimal)

The Dynojet 250 dyno is a Load Control dyno that basically makes the bike react as if it were on the road with a real rider on it by varying the load placed on the motor by using a huge electric brake that controls the force on the rotating dyno drum. By doing this it allows the tuner to determine the best possible Fuel mapping for not just full throttle, but for individual rpm & throttle position combinations (for example 5% throttle @ 4500 rpms) so you can tune for steady state cruise or roll-on acceleration as well as the typical full throttle run. Of course there are so many external variables involved inside the ECU's on todays current sportbikes, most of which revolve around passing EPA emissions testing, that it can be alot to compensate for when trying to get optimal performance out of your fuel injected bike. Just a side note: current technology can build engines that are so efficient they easily pass EPA emissions testing, what they have a hard time passing nowdays is the noise testing & yes the factories do alter the fueling in the ECU to help with the noise testing scenario too.

The majority of tuning all comes down to the Air Fuel ratio. Optimum power is generally around 12.6:1 while the stoichiometric value for a gasoline burning engine is about 14.6:1 for a good compromise of performance & mileage while Dynojet themselves generally target 13.2:1 when they build their own maps. The Dynojet 250 dyno has an O2 sensor as standard equipment & the tuning link software used in conjunction with a Powercommander (PCIIIr) can be set to achieve a user specified Air/Fuel ratio target number & the software will reprogram the Powercommander automatically in a series of sampling stages. These stages are set-up by the user and are basically compromises from one to the next unless of course you set the samples up identically.

The most important aspect to Dyno Tuning is the dyno operator! Finding a qualified dyno tuner is alot harder than it would seem. Just because a dyno operator has been to the Dynojet school & can run both the dyno & the tuning link software it does not automatically make him capable of tuning the RC properly or any other bike for that matter as each bike has its own nuances

There are so many little things that have to be accounted for, one of the main issues is engine temperature. With the current 3D mappings now on Fi bikes they respond drastically to temperature variations (especially Honda's with their auto enrichening ECU's that go super rich as the engine temp climbs) & if the dyno operator isn't making sure that he starts the consecutive runs giving sufficient time to get the engine back to the original temp of the baseline run then you can get extreme variances in horsepower up to 7-10 horsepower sometimes from as little as a 5 degree engine temperature change which can give you misleading tuning information if you are not watching for it (& that is just one example). People have asked for more in depth info on this subject so I'm going to add some more:

Current Honda ECU's automatically get richer as the engine temp increases the air/fuel ratio is changing constantly at a non linear rate.   For instance you may get the 100% perfect map developed for your bike on the dyno & let's say the engine is at 185 degrees, well at certain points in the rev range their are windows in the ECU where the mapping changes the mixture.  Let me give you some examples (these windows will be different for each model of bike & even the same model of bike can have different ECU eproms for various countries/regions)

168-172 degrees is a window
173-178 is a window
179-184 is a window
185-194 is a window
195-205 is a window
206-212 is a window
213-218 is a window

Each one of those windows has a different mapping forced by the ECU that alters the air fuel ratio of the bike & generally they get richer in steps (sometimes a window at a higher temp can also be leaner) so even though the PCIIIr map may be perfect for 186 degrees it may not be so great for 195 degrees & it then might be worse or better at even 206 degrees etc....

Now with the factory ECU already over rich it is very hard to find these windows even with a gas analyzer on a load control dyno, but once you add a Powercommander & get a good A/F ratio which produces better power & crisper throttle response then you may start to notice that the bike runs better at certain temps than others.  Even with the stock ECU you can tell if you know what to feel for.  You yourself may have noticed that at certain temps (harder to tell on bikes without a digital gauge) that the bike seems to run smoother & even shifts easier.

Additional notes:

Carburated bikes suffer less from this as they don't have external variables from the maps forcing them to change the mixture, but the dyno results can still be skewed by not paying attention to the outside variables during the run.

The Dynojet program is superb, but it is not perfect. The load control Dynojet 250 with the gas analyzer & interface that custom tunes the Powercommander units to any preset Air/Fuel ratio you choose at each individual rpm & throttle setting is a great tool for getting a base mapping done though it still cannot truly emulate real world loads on the motor & to get a truly optimal mapping you still need to fine tune your mapping by riding it on real roads. I prefer to use a Lamda sensor to get the A/F & tune from there, but still usually end up changing values beyond the scope of what the A/F ratio should be to cure drivability conditions, but again there is no better place than to start with a "professional dyno load base mapping well worth $200 or even $300 as long as the dyno operator knows what he is doing...

Also if you are paying for carb or mapping work ALWAYS make them show you the Air/fuel ratio charts! All to often I see these guys that pay some shop to make them a "custom" map & for their money they get a dyno chart that has two curves one higher than the other one, but the curves are 100% identical... This is usually indicative of fudging the correction factor on the dyno and or switching from DIN to SAE numbers etc... The Air/Fuel chart doesn't lie & if they made mapping changes it will show.

Some other things to note:

The PAIR valve system on all the new Honda's (& many other brands as well) injects fresh air into the headers. If you do not clamp off the tubes (or remove the entire PAIR system as many people do) before doing the dyno runs the exhaust gas analyzer will get false A/F readings of being overly rich.

Dyno testing in general can be very misleading & should only be used to show changes in power delivery on the same bike on the same dyno. Every dyno is different & will have different calibrations so you simply cannot compare dyno charts from two different dyno's & expect accurate results. In addition to the important & no so well known variables that I mentioned above such as the engine temp affecting the dyno results many other varaibles exist as well, Over-inflating your tires can yield higher numbers on the dyno and a well lubricated, properly adjusted chain will also insure better dyno results too...

I'll add more later as the need arises to cover more common questions & I get some typical feedback and/or questions about this page


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